Microscopic Visualization Of The Characteristics Of Gas Flooding Seepage Flow In Porous Media

Micro displacement visualization experiment is an important micro simulation technique to study the flow characteristics and motion laws of fluid in porous media.Visual simulation experiment can observe and study the characteristics of condensate oil and gas phase change from the perspective of reservoir microscopic pore structure,and study the process of remaining oil formation,the distribution of remaining oil,gas and water and the way of its migration and enrichment.In order to study the microscopic oil-water seepage characteristics of gas flooding process in porous media,laser etching model,sanding model and real sandstone model were designed for the experimental study of microscopic changes of condensate gas reservoir reverse condensation,and CO₂ flooding was studied through a real core model.A reasonable technical route was formulated for the research content,and the flow of different experiments was briefly described.During the experiment,high magnification microscopes were used for observation and image acquisition.After completing the experiment,representative image points were marked and the phase state was selected.A detailed analysis of displacement experiments led to the following understanding:?1?After the pressure drops below the dew point pressure,the condensate droplets are generated from the edge of the pores and the small slits in the three models,and they are continuously transported and aggregated to form a flake or slug oil.The presence of formation water also has an impact on the retrogradation of the condensate gas system,resulting in an increase in the saturation of the condensate.?2?Existence of remaining oil after conventional waterflooding is mainly in the form of thicker oil film,beaded string,and oil patch.After CO₂ flooding,the remaining oil mainly exists as a thin oil film,solitary droplets and small oil spots.?3?The injection of water-displacement simulation oil is mainly through displacement,stripping,and entrainment of oil in blisters.CO₂ miscible flooding mainly reduces the tension between the two phases through the miscibility effect.The CO₂ immiscible flooding can reduce the viscosity of oil and the volume of expanding oil.Through the above research,the microscopic seepage characteristics of gas flooding oil in the porous media and the mechanism of CO₂ displacement have been clarified,providing technical support for the establishment of an actual oil and gas reservoir development plan.